1. Field of the Invention
The present invention relates to a shuttering mechanism for a cassette and particularly relates to a shuttering mechanism requiring no strict dimensional accuracy and requiring no special mechanism in the cassette, wherein a shutter is automatically actuated to its closed position when the cassette is removed from a cassette holder without damage to the cassette.
2. Description of the Prior Art
Since such recording media as magnetic discs often become incapable of recording and playing back when dust or finger grease accumulate on the recording surface, magnetic discs are housed within a cassette to protect the recording surface from such contaminants. In addition, during recording or playback, a record/playback head comes into contact with the magnetic disc via a window built into the cassette. Furthermore, to prevent dust and such from entering the cassette and to prevent fingers from coming into contact with the surface of the magnetic disc via the window, a shutter is added to the cassette to expose and cover the window so that the record/playback head can be brought into contact with the magnetic disc when the shutter is in the open position when the cassette is in use.
However, if an operator fails to close the shutter when the cassette is taken out of the cassette holder, the shutter does not serve its function.
In a conventional shuttering mechanism, a spring is provided on the cassette to bias the shutter towards its closed position and the shutter is opened against the spring force when the cassette is inserted into the cassette holder for recording or playback. When the cassette is taken out of the cassette holder, the shutter is automatically closed due to the spring force.
However, this is disadvantageous in that the spring biasing the shutter toward its closed position adds to the size and weight of cassettes designated for use in small-sized light weight record/playback apparatus. In addition, it takes time to mount these extra parts on the cassette so that the cost of manufacturing such a cassette is increased. Since the cassette is mass-produced and used in large quantities, even a slight increase in the cost covers a large profit loss.
On the other hand, as disclosed in Japanese Patent Application Examined Open No. Sho 51-23,167 published on July 15, 1976, another shuttering mechanism has been proposed in which a swing lever is installed on the cassette holder; when one end of the swing lever is pushed by the cassette, the other end thereof is pivoted toward the cassette and engages a groove formed in the shutter, and as the cassette is then moved within the cassette holder, the shutter is opened or closed automatically.
However, this shuttering mechanism has a drawback. Since it is difficult to control the timing at which the free end of the swing lever moves toward the cassette, one end of the swing lever or the other may slide abrasively along the outer frame of the cassette if the timing is even slightly wrong. Since the outer frame of the cassette is usually made of a synthetic resin, resin dust generated due to abrasion by the swing lever may be deposited on the record/playback apparatus. This dust may subsequently get into the cassette and adhere to the recording surface of the magnetic disc.